Poly(vinyl trifluoroacetate) has commercial importance as a precursor to highly syndiotactic poly(vinyl alcohol) hydrogels, which themselves are commercially important as materials for, e.g., contact lenses, membranes, and as coatings for polymeric and non-polymeric substrates such as membranes. Heretofore, the polymerization of vinyl trifluoroacetate has posed a number of significant problems.
Bulk synthesis of poly(vinyl trifluoracetate) via free-radical polymerization has been described in U.S. Pat. No. 2,436,144 (assigned to duPont), but the method is not practical on a large scale due to the highly exothermic nature of the polymerization. Polymerization of vinyl trifluoracetate in common organic solvents has been described. Haas et al., Journal of Polymer Science, Vol. 22, p. 291 (1956), describe a reaction in acetone, resulting in a low-molecular weight material. Pritchard et al., Journal of Polymer Science, Part A-1, Vol. 4, p. 707 (1966) describe synthesis in n-heptane at 80.degree. C. with low conversion, and in carbon tetrachloride at -50.degree. C., also with low conversion. Harris et al., Journal of Polymer Science, Part A-1, Vol. 4, p. 665 (1966) describe a reaction in n-heptane at -78.degree. C. to give a high molecular weight polymer. Such low temperature reaction conditions are difficult to maintain on a commercial scale.
Polymerization of vinyl trifluoroacetate in inert chlorofluorocarbon solvents such as that available under the trademark FREON.TM. 113 has been described by Gagnon, et al. in U.S. Pat. application Ser. No. 07/775,969, filed Nov. 8, 1991, now abandoned, assigned to the assignee of the present invention, which is a continuation-in-part of the following U.S. patent applications Ser. Nos.: 07/605,754, 07/605,757, 07/605,828, 071605,834, 07/605,921 and 07/605,948, all filed Oct. 30, 1990, all now abandoned. A similar synthesis was described by Hammar et al. in U.S. Pat. No. 4,673,539, assigned to the assignee of the present invention, with the exception that Hammar et al. did not use trifluoroacetic anhydride as a water scavenger. Commercial use of such chlorofluorocarbon solvents is severely restricted for environmental reasons.
Copolymers of vinyl trifluoroacetate and acrylonitrile, produced in cyclohexene or hexane solutions, are described in U.S. Pat. No. 3,388,199 (Monsanto). However, incorporation of vinyl trifluoroacetate is unsatisfactory.